1. Field of the Invention
The present invention relates to a method of purifying exhaust gases and a catalyst for use in the exhaust gas purifying method.
2. Background Art
Typically, there have been known HC trapping type catalysts for purifying exhaust gases from a combustion apparatus for automobile engines. Such an HC trapping type catalyst comprises a trapping material that traps hydrocarbons (HC) in an exhaust gas at a lower temperature and releases HC trapped therein and a catalytic material that purifies HC released from the trapping material.
One of the HC trapping type catalysts, that is disclosed in, for example, Japanese Unexamined Patent Publication No. 9-872, comprises an HC trapping layer of β-type zeolite that is coated on a wall of a pour of a cordierite honeycomb substrate and a catalyst layer of a composite oxide of alumina and barium oxide with palladium carried on the composite oxide that is coated over the HC trapping layer. It is also disclosed in the publication mentioned above that an oxide containing Pr ions can be utilized as a NOx trapping material and an oxide containing cerium ions can be utilized as an oxygen absorption material.